This invention relates generally to the field of submersible fuel pumps for use in underground fuel storage tanks. More specifically, this invention relates to pump controllers and networks of fuel pumps used in conjunction with submersible fuel pumps to dispense fuel at service stations.
Most neighborhood gas stations provide a number of fuel pumps each capable of dispensing a variety of fuel grades. But while the gas station may have several fuel dispensers, these stations typically store fuel in only a few underground tanks. Most often the gas station will have only a few tanks for each fuel grade, and these few tanks will provide the fuel for that particular grade to all of the dispensers at the gas station that are capable of dispensing that grade of fuel.
Because only a few fuel tanks are providing the fuel for a number of dispensers, the pumps which actually draw the fuel out of the tanks are submerged within the fuel in the fuel tank itself. By placing the pumps inside the fuel tank, the overall number of pumps that have to be maintained is reduced. Furthermore, submersing the pump in the fluid itself allows the fuel to cool the pump motor. This allows for the use of higher capacity motors and pumps without requiring additional cooling systems.
Placing the pump inside the fuel tank has a number of drawbacks, however. Because the tanks are typically located under the pavement of the station, they are not readily accessible for maintenance or monitoring. Furthermore, submersing the pumps in the fuel requires that extra care be taken to prevent electrical malfunctions which could cause sparks or which could cause the pump motor to overheat, either of which may ignite the fuel or damage the pump motor.
Among the problems encountered most often with submersible pumps is that of dry-run operation. In this situation, the fuel level in the tank has fallen below the pump motor causing the pump motor to operate in the air. Because the cooling for submersible pumps is provided by the fuel itself, operating in the air can cause the motor to overheat. In addition, submersible pump motors are designed to provide optimum performance when they are pumping and operating in fuel, so prolonged dry-run operation can damage the pump motor.
To address these issues, most submersible pumps include pump controllers that monitor the operation of the pump. Conventional controllers provide monitoring for such operational characteristics as fluid leaks, pump failure, and pump and conduit pressure. These conventional controllers often require the use of sensors to provide the data for the monitored condition. While using sensors inside the pumps to monitor malfunctions can be cost-effective and allow for the monitoring of a wide variety of pumping factors, the life span or durability of these sensors is often far shorter than that of the pump itself. Furthermore, as more sensors are added to the pump to monitor possible malfunctions, the computer equipment required to process the information and relay it to the operator becomes more sophisticated. Finally, these conventional controllers require the operator to manually reset them after each malfunction has been corrected. This lengthens the time the pump is taken off-line as a result of a malfunction, and complicates the repair process for the operator and fuel station owner.
What is needed in the industry is a robust pump controller capable of detecting malfunctions and errors that arise during operation, but which does not use fragile sensor equipment and which can reset itself upon correction of the underlying malfunction.
The present invention addresses the above-mentioned problems associated with conventional pump controllers by providing a method of detecting faults in the fuel pumping process without the use of specialized sensors. In addition, pump controllers in accordance with the present invention can be networked or disposed together in a manifold to allow a number of pumps to work simultaneously or in turn in a single tank or across multiple tanks supplying the same fuel grade. This provides for pump redundancy in the event of pump failure or parallel operation in order to minimize extended use of any single pump or to supply large quantities of fuel to the dispensers during period of high demand.
Specifically, the present invention deals with the problem of dry-run operation by automatically shutting off the pump and signaling a dry-run alarm when the dry-run condition is detected. When new fuel is added to the tank, the controller is capable of detecting this condition and automatically resetting itself without user intervention.
In order to accomplish this automatic shutoff and automatic reset, the controller must be calibrated when it is installed. During the calibration, the pump motor is started, but no fuel is dispensed. A microprocessor in the controller samples the voltage, current, and phase between the voltage and current signals of the pump motor and stores these as the reference values. These values are compared against values measured during normal operation of the motor to detect the presence of faults.
Specifically, the phase value between the voltage and current signals of the motor is used to measure the power factor of the electrical motor. The power factor of the motor represents a ratio between the energy into the motor and the energy coming out of the motor. If the power factor is low, the motor is only putting out a fraction of the power put into it. When the power factor is low, the phase value will be high. Because the reference value for the phase is determined when the pump motor is operated in the presence of fuel, the phase value will only be higher than this reference value if the pump is operating in the absence of fuel. If this is the case, the controller will shut off the pump motor and signal the dry run condition alarm. An operator, human or otherwise, seeing this alarm will recognize that the fuel tank is low or empty.
Every time the fuel dispenser is activated, the controller momentarily reactivates the pump motor and samples the phase again. If fuel were added into the tank since the dry-run alarm was triggered, the phase value measured will then be below the reference value. The microprocessor will clear the alarm condition and reactivate the pump. If the phase value is still greater than the reference value, the pump motor is likely still operating in air, indicating that the tank is still empty. In this case, the controller will leave the alarm active.
In addition to detecting the dry-run condition of the pump, the process of monitoring the voltage signal, current signal, and phase of the pump motor allows the controller to monitor other pump characteristics as well. Because the controller is calibrated by operating the pump in the presence of the fluid to be dispensed, all that is required to setup the controller and pump for pumping a different fluid is to recalibrate the controller in the presence of that fluid. This way, the fuel grade, for example, dispensed from a particular tank can be changed without having to replace the controller.
In addition to detecting fault conditions, a pump controller in accordance with the present invention can be used in a network with other similar pumps and pump controllers in a single tank to provide tandem or redundant operation. When used in this way, a pump can automatically request additional pumps to come online if it is operating beyond its peak performance levels. This will occur when the demand for the fuel being pumped is high. Pumps can also automatically come online if other pumps in the network are deactivated due to dry-run conditions or some other fault.
In tandem operation, a number of pumps and controllers are used in a single fuel tank, or across multiple fuel tanks dispensing the same fuel grade, to provide fuel to the dispensers. The controller of an active pump will signal another pump in the network to begin pumping either when the required flow of fuel exceeds the first pump""s peak flow performance, or when the first pump is deactivated due to dry-run conditions or other malfunction.
The advantage of this network of pumps is that malfunctioning pumps will take themselves offline and request help from other pumps on the network without requiring any intervention by the operator. The remaining pumps in the network will automatically take over the task of dispensing fuel. Furthermore, this network allows the pumps to work in a masterless relationship rather than a master-slave relationship, which could fail entirely if the master pump went offline. The masterless network is also more scalable and fault-tolerant than the master-slave network.
Other purposes, uses, and features of the invention will be apparent to one skilled in the art upon review of the following.